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* [Bug tree-optimization/36343]  New: Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering
@ 2008-05-27 12:42 rguenth at gcc dot gnu dot org
  2008-05-27 12:46 ` [Bug tree-optimization/36343] [4.3/4.4 Regression] " rguenth at gcc dot gnu dot org
                   ` (11 more replies)
  0 siblings, 12 replies; 13+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2008-05-27 12:42 UTC (permalink / raw)
  To: gcc-bugs

extern void abort (void);

void __attribute__((noinline))
bar (int **p)
{
  float *q = (float *)p;
  *q = 0.0;
}

float __attribute__((noinline))
foo (int b)
{
  int *i = 0;
  float f = 1.0;
  int **p;
  if (b)
    p = &i;
  else
    p = (int **)&f;
  bar (p);
  if (b)
    return **p;
  return f;
}

int main()
{
  if (foo(0) != 0.0)
    abort ();
  return 0;
}


We TBAA-prune the points-to-set of p due to the dereference *p but use
the pruned points-to-set for computing the call-clobber variables which
causes f not to be call-clobbered.  Thus we return 1.0 from foo.  Oops.


-- 
           Summary: Wrong code due to bad TBAA pruning of points-to-sets and
                    use in call clobbering
           Product: gcc
           Version: 4.3.1
            Status: UNCONFIRMED
          Keywords: wrong-code, alias
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36343


^ permalink raw reply	[flat|nested] 13+ messages in thread
end of thread, other threads:[~2008-09-19 15:07 UTC | newest]

Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-05-27 12:42 [Bug tree-optimization/36343] New: Wrong code due to bad TBAA pruning of points-to-sets and use in call clobbering rguenth at gcc dot gnu dot org
2008-05-27 12:46 ` [Bug tree-optimization/36343] [4.3/4.4 Regression] " rguenth at gcc dot gnu dot org
2008-05-27 12:46 ` rguenth at gcc dot gnu dot org
2008-05-28 22:12 ` rguenth at gcc dot gnu dot org
2008-05-29 10:33 ` rguenth at gcc dot gnu dot org
2008-05-29 10:35 ` rguenth at gcc dot gnu dot org
2008-06-06 15:04 ` [Bug tree-optimization/36343] [4.3 " rguenth at gcc dot gnu dot org
2008-08-27 22:09 ` jsm28 at gcc dot gnu dot org
2008-09-17 14:47 ` rguenth at gcc dot gnu dot org
2008-09-17 15:08 ` ebotcazou at gcc dot gnu dot org
2008-09-17 15:12 ` rguenther at suse dot de
2008-09-19 15:06 ` rguenth at gcc dot gnu dot org
2008-09-19 15:07 ` rguenth at gcc dot gnu dot org

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